1. Field of the Invention
The present invention relates to a ball screw with cooling means and more particularly, a ball screw with high efficiency cooling means.
2. Description of the Prior Art
FIG. 1 shows cooling means for a conventional ball screw. As shown in FIG. 1, a tunnel like through pathway 11 is bored penetrating along the longitudinal direction of a screw bolt 10 so as to provide a path for a cooling liquid thereby carrying away the heat of the screw bolt 10 imparted by the screw nut 12 and the circulating steel balls. It is well known to men skilled in the art that the operating principle of a ball screw and nut assembly is the screw nut 12 engaging a work piece or a working platform moves along the lengthwise direction of the screw bolt 10 by spirally rotation of the screw nut 12 with respect to the screw bolt 10. The screw nut 12 is coaxially sleeving over the screw bolt 10 and both structures are coupled with two threaded grooves each formed on the inner surface of the screw nut 12 and the outer surface of the screw bolt 10 respectively with a plurality of rolling balls interposed therebetween. By so the work piece or the working platform is able to perform its work by moving along the lengthwise direction of the screw bolt 10. In fact, owing to the fact that it is the screw nut 12 that actually carries the load of the work piece or the working platform and always in contact with the rolling balls so that its heat dissipation is difficult. On the contrary, the screw bolt 10 is constructed far longer than the screw nut 12 so that a major part of it is exposed to the air with a good air cool effect. Therefore, to form a cooling agent path along the lengthwise direction of the screw bolt 10 for heat dissipation as that has been commonly practiced in conventional techniques is definitely nonsense as putting the cart before the horse. Besides, forming a through pathway 11 coaxially along the longitudinal direction in a slim screw bolt 10 accurately requires a very fine technique to perform, a slight inadvertent alignment of center position may cause vibration of the screw bolt 10 during operation, or to the worst, result in cracking of the screw bolt 10.
In view of the foregoing situation, the inventor of the present invention herein conducted intensive research based on many years of experience gained through professional engagement in the manufacturing of related products, with continuous experimentation and improvement culminating in the development of efficient cooling means for ball screw of the invention herein.
Instead of boring a longitudinal through pathway for cooling agent along the screw bolt situated at better cooling condition, a cavity is formed between an outer cover and the screw nut as a pathway for cooling agent so as to deprive the screw nut of heat generated therein. Leak proof means such as several O rings are provided between the outer cover and the screw nut to prevent the cooling agent from leaking out of the cavity. To assure a better cooling effect, portion of the wall of the screw nut adjacent to the outer cover is pared partially in planar or curved surface to enlarge the space of the cavity and reduce the wall thickness of the screw nut thereby improving the cooling effect. Furthermore, a guiding tube spirally encircling the screw nut, or reciprocating in the longitudinal direction of the ball screw axis on the screw nut, is provided for guiding the cooling agent therein so as to prevent leaking of cooling agent.